The present invention relates to copper or a copper alloy reduced in α-ray emission and a bonding wire obtained by using, as its raw material, the foregoing copper or copper alloy which is used in the production of semiconductors.
Generally speaking, copper is a material that is used for the production of semiconductors, and is particularly the main raw material of copper or copper alloy wiring lines, copper or copper alloy bonding wires, and soldering materials. Upon producing a semiconductor device, copper or copper alloy wiring lines, copper or copper alloy bonding wires, and soldering (Cu—Ag—Sn) materials are used for bonding or sealing Si chips of IC or LSI to a lead frame or a ceramic package, during TAB (tape automated bonding) or for forming a bump upon producing a flip chip, or as a wiring material for semiconductors.
Recent semiconductor devices have high densification and lower operating voltage and cell capacity, and there is greater risk of soft errors caused by the influence of α rays emitted from materials positioned near semiconductor chips. Thus, there are demands for achieving higher purification of copper and copper alloys, and materials reduced in α-ray emission are also demanded.
While these are about a different material from the present invention, there are several disclosures related to the reduction of α rays; that is, disclosures related to the technology for reducing α rays from tin. These are introduced below.
Patent Document 1 describes a method of producing low α-ray tin by alloying tin and lead having an α-ray emission of 10 cph/cm2 or less, and thereafter eliminating the lead contained in the tin via refining. The object of this technology is to reduce the α-ray emission by diluting the 210Pb in the tin by adding high-purity Pb.
Nevertheless, in the foregoing case, a complex process of adding Pb in the tin and thereafter eliminating Pb is required. While a numerical value showing a considerable decrease in the α-ray emission is indicated 3 years after the tin is refined, this can also mean that this tin reduced in α-ray emission cannot be used until after the lapse of 3 years, and therefore it cannot be said that this is an industrially efficient method.
Patent Document 2 describes that the radiation α particle count can be reduced to 0.5 cph/cm2 or less when 10 to 5000 ppm of a material selected from Na, Sr, K, Cr, Nb, Mn, V, Ta, Si, Zr, and Ba is added to a Sn—Pb alloy solder.
Nevertheless, even with the addition of the foregoing materials, the radiation α particle count could only be reduced to a level of 0.015 cph/cm2, and this is not a level that is promising as today's semiconductor device material.
An additional problem is that elements such as alkali metal elements, transition metal elements and heavy metal elements, which are undesirable to get mixed into the semiconductor, are being used. Accordingly, there is no choice but to say that this is a low-level material as a material for use in the assembly of a semiconductor device.
Patent Document 3 describes reducing the count of radiation α particles, which are emitted from the ultrafine solder wires, to be 0.5 cph/cm2 or less, and using such solder wires as the connection wiring lines of a semiconductor device. Nevertheless, with this level of the radiation α particle count, this is not a level that is promising as today's semiconductor device material.
Patent Document 4 describes that it is possible to obtain high-purity tin with a low lead concentration and in which the α-ray count of lead is 0.005 cph/cm2 or less by using, as the electrolytic solution, highly refined sulfuric acid and hydrochloric acid such as high-grade sulfuric acid and high-grade hydrochloric acid, and performing electrolysis by using the high-purity tin as the positive electrode. If high-purity raw materials (reagents) are used by disregarding costs, it goes without saying that high-purity materials can be obtained. Even still, the lowest α-ray count of the deposited tin indicated in the Examples of Patent Document 4 is 0.002 cph/cm2, and this is not a promising level considering the high cost.
Patent Document 5 describes a method of obtaining metal tin of 5N or higher by adding nitric acid to a heated aqueous solution doped with crude metal tin so as to precipitate metastannic acid, filtering and washing the metastannic acid, dissolving the cleaned metastannic acid with hydrochloric acid or hydrofluoric acid, and using the obtained solution as the electrolytic solution to perform electrowinning. While this technology vaguely describes its application to use in semiconductor device, Patent Document 5 makes no particular reference to the limitation on radioactive elements and the radiation a particle count, and it could be said that Patent Document 5 does not have much interest in these issues.
Patent Document 6 describes technology of reducing the amount of Pb contained in Sn configuring the solder alloy, and using Bi or Sb, Ag, Zn as the alloy material. Nevertheless, in the foregoing case, even if Pb is reduced as much as possible, Patent Document 6 fails to specifically indicate a means for fundamentally resolving the problem of the radiation α particle count caused by Pb that naturally gets mixed in.
Patent Document 7 discloses tin having a grade of 99.99% or higher and in which the radiation α particle count is 0.03 cph/cm2 or less produced by using a high-grade sulfuric acid reagent and performing electrolysis. In this case also, if high-purity raw materials (reagents) are used by disregarding costs, it goes without saying that high-purity materials can be obtained. Even still, the lowest α-ray count of the deposited tin indicated in the Examples of Patent Document 7 is 0.003 cph/cm2, and this is not a promising level considering the high cost.
Patent Document 8 describes lead, as a brazing filler material for use in semiconductor devices, having a grade of 4N or higher, a radioisotope of less than 50 ppm, and a radiation α particle count of 0.5 cph/cm2 or less. Moreover, Patent Document 9 describes tin, as a brazing filler material for use in semiconductor devices, having a grade of 99.95% or higher, a radioisotope of less than 30 ppm, and a radiation α particle count of 0.2 cph/cm2 or less.
The toleration level of the radiation α particle count in all of these Patent Documents is lenient, and there is a problem in that they are not of a level that is promising as today's semiconductor device material.
In light of the foregoing circumstances, the present applicant proposed, as described in Patent Document 10, eliminating the influence of the α rays on semiconductor chips by using high-purity tin; that is, tin having a purity of 5N or higher (provided that the gas components of O, C, N, H, S and P are excluded), and particularly causing the respective contents of U and Th, which are radioactive elements, to be 5 ppb or less, and the respective contents of Pb and Bi, which emit radiation α particles, to be 1 ppm or less. In the foregoing case, the high-purity tin is ultimately produced by being subject to melting/casting, and rolling/cutting as needed, and this technology can cause the α-ray count of the high-purity tin to be 0.001 cph/cm2 or less.
Upon refining Sn, Po has extremely high sublimability, and when heated in the production process; for instance, during the melting/casting process, Po becomes sublimated. It is considered that, if the isotope 210Po of polonium is eliminated in the initial stages of the production process, the decay from the isotope 210Po of polonium to the isotope 206Pb of lead will not occur, which in turn will not cause the generation of α rays.
This is because the generation of α rays during the production process was considered to occur during the decay from the 210Po to the isotope 206Pb of lead. Nevertheless, in reality, even though it was considered that Po had been nearly eliminated during the production process, the generation of α rays continued to occur. Accordingly, it could not be said that the fundamental problem could be resolved merely by reducing the α-ray count of the high-purity tin during the initial stages of the production process.
While the foregoing Patent Documents are mainly related to the α rays of tin, copper or copper alloy is used as a wiring line material of LSI and a bonding wire for connecting the chip and lead frame in semiconductors. Since bonding wires are placed at a distance from the memory portion which causes soft errors, not much consideration was given to the α-rays amount that is emitted from the wires, and a level of 0.5 cph/cm2 or less was considered to be sufficient (refer to paragraph 0004 of Patent Document 11).
While there are some other Patent Documents related to copper or copper alloy bonding wires, none of them offer any disclosure related to the α-ray emission. Patent Documents related to copper or copper alloy bonding wires are listed below and briefly described.
Patent Document 12 describes a method of producing high-purity copper for a bonding wire of a semiconductor device, and describes improving the Vickers hardness, elongation and breaking strength by causing the total content of unavoidable impurities to be 5 ppm or less, and causing the contents of S, Se and Te contents among the unavoidable impurities to be respectively 0.5 ppm or less, 0.2 ppm or less, and 0.2 ppm or less.
Patent Document 13 describes, as a method of producing a copper material for a bonding wire, a refining process of electrolytic refining→vacuum melting→floating zone technique.
Patent Document 14 describes a bonding wire containing Fe, P, and In, and at least one type among Sn, Pb and Sb.
Patent Document 15 describes a method of producing a bonding wire material with an adjusted solidification rate as the method of producing a bonding wire material for a semiconductor element.
Patent Document 16 describes a bending-resistant copper alloy having high strength and high electric conductivity for a conducting wire or a cable, and further describes that the copper alloy contains Fe, P, and two types selected among In, Sn, Pb and Sb, and further contains Zr.
Patent Document 17 describes a copper alloy having high thermal resistance and high electric conductivity, and further describes that the copper alloy contains Fe and P, two types selected among In, Sn, Pb and Sb, and Zr.
In addition, as the copper refining method, Patent Document 18 describes technology of separating the anode and the cathode with a diaphragm, extracting the Cu ion-containing electrolytic solution eluted from the anode, and passing the electrolytic solution through an active carbon filter with an aperture of roughly 0.1 μm immediately before placing the electrolytic solution in the cathode box; Patent Document 19 describes technology, on the premise of achieving higher purification based on electrowinning or electrolytic refining, eliminating impurities from the anolite of the copper-containing solution based on acid and active carbon treatment, and using the high-purity copper solution, from which impurities have been eliminated, as the catholite; and Patent Document 20 describes technology of using a diaphragm cell in which a positive electrode (anode) chamber and a negative electrode (cathode) chamber are separated by a diaphragm, using a chalcopyrite leaching solution as the electrolytic solution in a chlorine bath and supplying the chalcopyrite leaching solution to the cathode chamber, and collecting electrolytic copper on the cathode surface based on electrolytic reduction.
Nevertheless, none of the foregoing copper refining methods disclose technology of reducing α rays.    Patent Document 1: Japanese Patent No. 3528532    Patent Document 2: Japanese Patent No. 3227851    Patent Document 3: Japanese Patent No. 2913908    Patent Document 4: Japanese Patent No. 2754030    Patent Document 5: JP H11-343590A    Patent Document 6: JP H9-260427 A    Patent Document 7: JP H1-283398 A    Patent Document 8: Japanese Patent No. S62-47955    Patent Document 9: Japanese Patent No. S62-1478    Patent Document 10: WO2007-004394    Patent Document 11: JP 2005-175089 A    Patent Document 12: Japanese Patent No. H7-36431    Patent Document 13: Japanese Patent No. H8-23050    Patent Document 14: Japanese Patent No. S62-56218    Patent Document 15: JP S63-34934 A    Patent Document 16: JP S62-214145 A    Patent Document 17: JP S61-76636 A    Patent Document 18: Japanese Patent No. 4620185    Patent Document 19: Japanese Patent No. 4519775    Patent Document 20: JP 2005-105351 A